Regina Hicks was supposed to pick up her 4-year-old son, Montana, from the home of her estranged husband's friend in Willard, Ohio -- but he said she never showed. Soon after her disappearance on the evening of Oct. 18, 2001, investigators found the 25-year-old's dead body in her white Camaro, submerged in a nearby pond, beginning a decades-long search to unmask her killer. A new "20/20" episode, " The Secret in the Water " a i ri ng Friday, May 1, at 9 p.m. ET on ABC and streaming the next day on Disney+ and Hulu, examines the case.   You can also get more behind-the-scenes of each week's episode by listening to "20/20: The After Show" weekly series right on your 20/20 podcast feed on Mondays, hosted by "20/20" co-anchor Deborah Roberts. Regina first started dating Paul Hicks when they were in high school, eventually marrying. He filed for divorce the day after she went missing, according to court documents. Regina Hicks is pictured here in a high school yearbook photo.…